The present invention relates generally to feed networks for multiterminal antennas and more particularly to feed networks which are independent of a common ground for multiterminal antennas.
There are currently many uses for multiterminal antennas, such as, communication, navigation, direction finding and remote sensing. These antennas, such as, planar and conical spiral antennas, and other multiterminal antennas typically rely upon a dedicated feed network for the excitation required in order to transmit or detect electromagnetic radiation.
There have been a variety of proposed feed networks for multiterminal antennas. Foremost among these feed networks are those in which each terminal of the multiterminal antenna is fed from a common ground point. A typical manner in which this type of feeding from a common ground point is accomplished is by feeding the multiterminal antenna from a number of coaxial cables wherein the number of coaxial cables is equal to the number of terminals. A center conductor from each coaxial cable is affixed to a terminal of the multiterminal antenna such that each coaxial cable feeds a single terminal of the antenna. The grounded shields of each coaxial cable are thereinafter brought into contact with the other grounded shields of the coaxial cables such that a common ground in established amongst the plurality of coaxial cables.
This manner of feeding a multiterminal antenna wherein each terminal is fed separately and a common ground point for the feeding network is established limits the broadband performance of the antenna. These limitations are typically caused by an absence of a broadband impedance match and the poor realization of a common ground point reducing balun performance.
Therefore, it would be desirable to provide a feed network for a multiterminal antenna in which the excitation of the antenna terminals is provided independent of common ground so that the antenna is capable of providing wider band width performance. Furthermore, it would be desirable to provide a feed network for a multiterminal antenna which is capable of transforming a feed from a plurality of coaxial cables to a plurality of twin lead conductors prior to their electrical connection to the terminals of the antenna.